The control of glucose 1,6-bisphosphatase by Ca2+ and calmodulin.

1. The control of glucose 1,6-bisphosphatase activity, the enzyme that degrades glucose 1,6-bisphosphate, a metabolite that regulates hexose phosphate metabolism, has been examined in a rat muscle extract. 2.

The control of glucose 1,6-bisphosphate by developmental state and hormonal stimulation in cultured muscle tissue.

1. The concentration of glucose 1,6-bisphosphate, a potent regulator of muscle glucose metabolism, was examined in embryonic muscle cells in culture. 2.

The effect of different patterns of long-term stimulation on contractile properties and myosin light chains in rabbit fast muscles.

Fast rabbit skeletal muscles (tibialis anterior and extensor digitorum longus) were stimulated for 2-28 days by electrodes implanted in the vicinity of the peroneal nerve to produce maximal contractions at two different frequency patterns: that occurring naturally in nerves to slow muscles (10 Hz continuously) or three bursts of tetani (40 Hz) per minute, each 5s in duration. Both types of frequency produced muscles more resistant to fatigue during isometric twitch contractions, and led to a prolongation of contraction time greater and more consistent with 10 Hz than with 40 Hz. The twitch/tetanus ration was significantly higher in muscles stimulated at 10 Hz for 3-4 weeks but was not different from controls in muscles stimulated at 40 Hz.

A method for quantitative extraction of enzymes and metabolites from tissue samples in the milligram range.

A method is described for quantitative extraction of soluble enzyme activities from tissue samples in the milligram range. Mechanical disintegration of the frozen tissue is performed in a micromortar from which the powdered tissue can be quantitatively transferred for extraction in small volumes within a microcentrifuge tube.

The breakdown of phosphatidylinositol in myoblasts stimulated to fuse by the addition of Ca2+.

1. The fusion of chick-embryo myoblasts to produce myotubes was studied. The myoblasts were grown for 50 h in medium containing 10--20 microM-Ca2+; during this period they achieve fusion competence.

A comparative microphotometric study of succinate dehydrogenase activity levels in type I, IIA and IIB fibres of mammalian and human muscles.

Activity levels of succinate dehydrogenase (SDH) were determined kinetically by means of comparative microphotometric measurements in situ. Activities were correlated with fibre types classified histochemically according to Brooke and Kaiser (1970). Analyses of tibialis anterior muscles in the mouse, rat, guinea pig, rabbit, cat and the human showed pronounced variations in the activity profiles of type I, type IIA and IIB fibres of these muscles.

A comparison of two ATPase based schemes for histochemical muscle fibre typing in various mammals.

A comparative study was performed on the fibre populations in tibialis anterior muscles of mouse, rat, guinea pig, rabbit, cat and dog using the two different methods of histochemical staining for myofibrillar ATPase after acid (Brooke and Kaiser 1970) or alkaline preincubations (Guth and Samaha 1970). For all species a complete correspondence existed between type I (Brooke and Kaiser 1970) and beta fibres (Samaha et al. 1970).

Succinate dehydrogenase activity in fibres classified by myosin ATPase in three hind limb muscles of rat.

1. Succinate dehydrogenase (SDH) activity was assessed in situ in single fibres of cross-sectioned extensor hallucis longus, extensor digitorum longus, and soleus muscles of rat by means of microphotometric recordings of initial maximum reaction rates. 2.

Ipsi-and contralateral changes in rabbit soleus myosins by cross-reinnervation.

Cross reinnervation of soleus muscle in the adult rabbit induces changes in myosin light chain and isomyosin patterns. The transformation of the light chain pattern consists of a decrease in LC1's and LC2, and an induction of the three fast type myosin light chains. The transition in the isomyosin pattern consists of a decrease of the slow type isomyosin SM and an induction of fast type isomyosins FM1, FM2, and FM3 normally seen in fast-twitch rabbit muscle.

Electrophoretic analyses of myofibrillar proteins from the body wall muscles of Ascaris suum.

A myofibrillar protein extract has been isolated from the muscle of Ascaris suum. Two-dimensional electrophoresis of this extract revealed that the myosin light chain 1 (ALC1) migrates as 3 components with approximate isoelectric points in the range of 5.3-5.

Correlation between ultrastructural and functional changes in sarcoplasmic reticulum during chronic stimulation of fast muscle.

Chronic indirect stimulation of fast twitch rabbit muscle (tibialis anterior and extensor digitorum longus) with a frequency of 10 Hz induced a progressive transformation of the sarcoplasmic reticulum (SR). Ultrastructural changes as studied by electron microscopy of freeze-fractured vesicles consisted in a decrease of intramembranous particles of the concave (A) face and an increase of particles in the convex (B) face. The asymmetry of the membrane proved to be lowered.

Microphotometric measurement of initial maximum reaction rates in quantitative enzyme histochemistry in situ.

Final reaction product formation was recorded microphotometrically for succinate dehydrogenase in cross-sectioned muscle fibers at initial rate conditions and during prolonged incubations. Incubations with gel films and aqueous reaction medium both showed a decline of reaction rates. Maximum reaction rates could only be determined at initial rate conditions during the first minute of the incubation.

Comparison of enzyme activities among single muscle fibres within defined motor units.

1. Muscle fibres from single motor units of rat extensor digitorum longus were depleted of their glycogen by electrical stimulation and identified by the periodic acid-Schiff stain after treatment in a medium that selectively enhanced glycogen content in the non-depleted fibres. 2.

Do enzyme activities vary along muscle fibres?

Distribution of succinate dehydrogenase activity along muscle fibres has been studied qualitatively by histochemistry on single micro-dissected rat muscle fibres and quantitatively by comparative kinetic microphotometry on longitudinal muscle sections. Qualitative staining reactions showed no appreciable variations in enzyme activity along the fibres regardless of fibre type. By quantitative assessment, minor variations were found along fibres but were within the range of the experimental error.

Characterization of cardiac microsomes from spontaneously hypertonic rats.

Capacity of Ca2+ sequestration was found to be significantly lowered in microsomal preparations of hearts from spontaneously hypertonic rats. A decrease to 40% of the control level was found for basal and extra ATPase. A similar reduction existed in initial and total Ca2+ uptake.

Microphotometric studies on intraacinar enzyme distribution in rat liver.

Intraacinar distribution of succinate dehydrogenase (SDH), malate dehydrogenase (MDH), NADP-dependent isocitrate dehydrogenase (IDH), glutamate dehydrogenase (GluDH), lactate dehydrogenase (LDH) and NADH-tetrazolium dehydrogenase (TR) was studied in rat liver cryostat sections by multipositional microphotometric activity determinations. By statistical evaluation, activity of individual enzymes could be related to the acinar topography. Activity was evaluated with regard to distance of measuring position either from afferent (portal) or efferent (hepatic) vessels.

Kinetic microphotometric activity determination in enzyme containing gels and model studies with tissue sections.

The dependence of microphotometrically recorded reaction rate on local enzyme concentration was studied as a basic prerequisite of comparative microphotometric enzyme activity determinations at initial rate conditions in tissue sections. Polyacrylamide gels containing defined concentrations of glucose-6-phosphate dehydrogenase served as a model. Optimal conditions of preparing enzyme containing gels are reported.

Principle and method of kinetic microphotometric enzyme activity determination in situ.

An advanced apparative set-up is described for multipositional microphotometric recording of histochemical enzyme reactions in cryostat sections. It consists of a computer controlled microscope photometer with scanning stage. Measurements on the same tissue section may be performed at 12 preselected positions.

Metabolic heterogeneity of muscle fibers classified by myosin ATPase.

Muscle fibers are commonly classified histochemically into three types by the staining intensity for myosin ATPase combined with those for metabolic enzymes. Preincubation at pH 4.6 gives rise to three staining intensities of myosin ATPase which are also used for fiber typing.